This invention claims the benefit of Japanese patent Application No. HEI 10-305781, filed on Oct. 27, 1998, which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a lamp and, more particularly, to a projection type headlamp for a vehicle in which a projection lens is disposed such that a focus point of the projection lens corresponds to a second focus point f2 of an elliptic reflection surface. A light distribution pattern of the headlamp is defined by projecting a cross-sectional luminous flux and converging it into the second focus point f2.
2. Discussion of the Related art
FIG. 8 illustrates a conventional projection type headlamp in which a light source 92 is located close to a first focus point f1 of a reflector 91. The reflector 91 is circular as viewed from the front with an elliptically shaped surface as viewed from the side forming an opening. A projection lens 93 is disposed adjacent the opening in the reflector 91. The lens 93 has a focus point f3 located close to a second focus point f2 of the reflector and into which light emitted from light source 92 converges.
Of the many light rays that converge into the second focus point f2, only light rays having an appropriate cross-sectional orientation for forming the specific light distribution pattern for the head lamp 90 can pass through the projection lens 93. Other light rays are prohibited from passing through the projection lens 93 by a shade 94.
However, the light from the light source 92 converges into the second focus f2 and diffuses and radiates through the projection lens 93 toward the direction of irradiation for the headlamp 90. Accordingly, the light will diffuse in a radiating direction after the light passes through the projection lens 93.
Therefore, the conventional projection type lamp 90 has a light distribution pattern whose shape is easily determined, but whose luminous intensity distribution can not be freely determined because it is substantially impossible to concentrate or distribute light rays at predetermined positions due to the diffusing characteristic which are maintained even after the light rays pass through the projection lens 93. Specifically, it is difficult to form a light distribution pattern for high beam mode because it requires a large amount of light directed outwardly from the front of the vehicle to provide long distance visibility in the high beam mode.
The conventional projection type headlamp 90 and the projection lens 93 are formed in a circular shape as seen from the front of a vehicle. This type of circular projection lens 93 is unsuitable for current design trends in automobile body design. To meet current design requirements, it is sometimes preferred to cut of the upper and lower portions of the projection lens 93. In this case, the amount of light passing through the lens decreases and lowers a driver""s ability to see when using the headlamp.
The invention is directed to a projection type lamp that substantially obviates one or more of the above problems due to the limitations and disadvantages of the conventional projection type lamps.
According to the invention, the above objects are achieved by providing a projection type headlamp including an oval projection lens with a long horizontal diameter, a light source, and a reflector. The oval projection lens can be shaped such that the lens includes two substantially similar to sphericallens portions formed by dividing a substantially hemispherical lens into two parts at its diameter and attaching the similar to sphericallens portions to opposite ends of a semi cylindrical lens portion. The longest width of the oval projection lens is called a horizontal diameter in this specification since the lens is intended to be mounted on a vehicle with the horizontal width substantially parallel to the travel surface for the vehicle. The semi cylindrical lens portion has a focus line extending in the horizontal direction.
The reflector can be elliptically shaped and include a first focus point located close to the light source in a vertical cross-sectional view, and a second focus point located close to the focus line in a horizontal cross-sectional view. In addition, a free curved surface on the reflector can provide a predetermined horizontal irradiation angle to the light emitted from the light source. The width of the free curved surface can be the same as that of the semi cylindrical lens portion in the horizontal direction.